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Car Forum / Mercedes-Benz Cars / February 2005Rear End Wiggle on Acceleration
I have a 1987 300E (not 4matic). When accelerating, the car pushes to the left. When I let off the gas, it pulls back to the right. The pull back to the right can be quite sudden and a little unnerving in bad weather. The more power being applied, the more noticeable this is. It feels like one of the rear wheels is moving under thrust. If I had to guess, I would say it feels like the right rear wheel is being pushed backward. I have had the car on a lift and checked the bushings in all those arms that hold the rear wheels in place. There didn't seem to be much movement to me. I have also had a 4 wheel alignment and the print out shows the toe is very good on all 4 wheels. None of the brake calipers seems to be binding. I think that one or more of those arms in the rear need to be replaced. Is there any way to figure out which one(s) are worn out? Could something else be causing this problem? Thanks, Robert A. Possible bent rear control arm - that changes its rear wheel's toe in as the rear "squats" during acceleration - would cause the slewing problem. Deceleration reverses the process PLUS you are already steering against the abnormality so the directional change is magnified. This will be tough to diagnose because the toe in changes - deliberately by design - as the car's body height changes vs. the axle. B. Older car may have been wrecked during its 18 years of travels. Body may be distorted causing the same effect as in A. C. Look for abnormal rear tire wear - loss of tread depth on one side of the tire. That's the side of the car with the problem. > A. Possible bent rear control arm - that changes its rear wheel's toe > in as the rear "squats" during acceleration - would cause the slewing [quoted text clipped - 9 lines] > C. Look for abnormal rear tire wear - loss of tread depth on one side > of the tire. That's the side of the car with the problem. TG's comments are right on as usual. Also it brings to mind something else... how much do you weigh if you don't mind my asking? Marty I am average height and weight. The car does not appear to have been wrecked. The underside is amazingly pristine. The rear springs do have considerable sag. I have replacements on hand waiting to be installed. Could weak springs cause this? How would I diagnose a bent control arm? Thanks, Robert >> A. Possible bent rear control arm - that changes its rear wheel's toe >> in as the rear "squats" during acceleration - would cause the slewing [quoted text clipped - 19 lines] > > Marty The rear suspension's toe in is not adjustable via a cam bolt etc. but is adjusted by having the correct chassis height vs. the axle. The springs fit into hard rubber pads or cups whose thickness is made to achieve the car's correct riding height. You need to read about this in the car's repair manual or CD-ROM, particularly since you will be installing replacement springs. The springs are coded as to their length and the respective rubber pad or cup that supports the spring ought to be the correct one or the spring replacement job will be for naught. If you lack this information perhaps you ought to visit the parts man at the local dealer who may be able to help you match the springs you have to install to the correct rubber pad or cup. Lacking the toe in vs chassis height parameters of a perfect control arm I don't know how to diagnose a bent control arm. Install the replacement springs to achieve the correct height and see if that fixes it, if not, then deal with the control arms. |
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